This invention relates generally to spring-assisted shift apparatus. More particularly, it relates to such apparatus which may incorporated into the shift mechanism of a multi-speed gear box, such as an automotive four-wheel-drive transfer case, which uses a rotatable cam to move shift forks in order to select various operating modes.
In recent years there have been many improvements in automotive drive trains, including improvements relating to transfer cases which provide high- and low-speed ranges in conjunction with two- and four-wheel-drive operating modes. The typical shift apparatus for such a transfer case requires that the vehicle operator move a shift lever to select one of the operating modes. The teeth of a gear set, jaw-clutch assembly or the like must be moved into meshing relationship in order to effect engagement.
It sometimes happens that the teeth abut when engagement is attempted, thus blocking completion of the shift. In order to complete the shift, it is necessary for the operator either to rotate one of the toothed members slightly and then attempt to shift again, or to continue applying pressure to the shift lever while rotating one of the toothed members. The latter is the more expedient method, but often is difficult for the operator to accomplish. This is particularly true if the shift is into the four-wheel-drive, low-range operating mode, as this typically is the situation in which severe driving conditions are encountered.
Thus, there is a need in the art for shift apparatus which provides an assist mechanism in order to insure that engagement in the desired operating mode will be completed once the shift has been initiated. This allows the operator to direct his attention elsewhere, secure in the knowledge that the selected operating mode is engaged.